1. Field of the Invention
The present invention relates to traffic lane deviation preventing systems, and more particularly to a traffic lane deviation preventing system that determines a possibility of its vehicle's deviation from a traffic lane and automatically carries out deviation preventing control.
2. Description of the Related Art
In recent years, traffic lane deviation preventing techniques have been developed. According to such techniques, in order to prevent a vehicle from deviating from either the right or left traffic line of the traffic lane that the vehicle takes and crossing over or entering the adjacent lane, a region ahead of the vehicle is image-sensed using a CCD (Charge Coupled Device) camera or the like to detect the traffic lane and a possibility of traffic lane deviation is determined (see for example JP-A-2003-16593).
Various kinds of traffic lane deviation preventing systems that have been suggested automatically have a vehicle returned to the lane the vehicle should take at the present by activating self steering control when a possibility of traffic lane deviation is determined (see for example JP-A-7-129897, JP-A-2001-39326 (e.g., see also, U.S. Pat. No. 6,473,678), and JP-A-2004-231096).
According to conventional traffic lane deviation preventing techniques, a travel target point is set a prescribed distance ahead of the vehicle on a line extending in the vertical direction to a traffic line, and the vehicle moves toward the travel target point by self steering control, so that the vehicle is returned to the present traffic lane.
According to the traffic lane deviation preventing technique, the travel target point is often set in the center of the traffic lane, in other words, at a point equidistant from the right and left traffic lines. If the self steering control is carried out to make the vehicle follow the travel target point set in this manner, however, the steering wheel is abruptly turned in the opposite direction upon determination of deviation as shown in FIG. 20, and the yaw rate and steering wheel torque of the vehicle significantly change.
Therefore, the driver feels awkward as if the vehicle is forcibly pulled back and changed in the position. After the vehicle is pulled back, the vehicle can meander between the right and left with respect to the center of the traffic lane by overshoot.
Furthermore, according to some conventional traffic lane deviation preventing techniques, a vehicle on the verge of deviating from a traffic line has its advancing direction returned simply horizontally to the traffic line or changed in an averting direction or force is gradually provided to move the vehicle in the averting direction so that the time before the deviation is simply prolonged. According to the methods, however, the vehicle is allowed to move simply near the line from which the vehicle is likely to deviate as shown in FIG. 21 and lane deviation cannot sufficiently be prevented.